Overview of the Invasive Weed Species Eriochloa villosa (Thunb.) Kunth and Its Management in Europe

Abstract

The wooly cupgrass (Eriochloa villosa) is an invasive weed species originating from East Asia that rapidly expanded into agricultural and disturbed land. Its tolerance to herbicides and ecological adaptations enable it to become persistent and difficult to remove with limited control methods. This review synthesizes existing research on its distribution, biology, biochemistry, ecology, management and agricultural impact. Lipid synthesis inhibitor herbicides are reported to provide good results when applied early. Others such as Nicosulfuron and Foramsulfuron, although still effective in many populations, have been linked to emerging resistance in others. Chemical control is still widely used and developing resistance is an increasing concern, so various other control methods are also discussed and encouraged. Row crops such as corn (Zea mays) and soybeans (Glycine max) are particularly vulnerable. Despite being problematic, this species presents potential as a medicinal plant as well as in phytoremediation. Regardless, numerous research gaps remain, particularly in chemical control, its economic impact, biochemical properties, community dynamics and distribution. We aim to provide a comprehensive basis for future research with a focus on interdisciplinary approaches in order to contain its spread as much as possible, as well as explore the benefits it may provide.

1. Introduction

Eriochloa villosa (Thunb.) Kunth, commonly known as the wooly cupgrass, is an increasingly problematic invasive weed species native to East Asia, believed to have been artificially introduced to new territories via agricultural machines and grain transportation [1,2,3,4]. The wooly cupgrass has the potential to cause important damage to agrosystems and biodiversity due to its ecological plasticity and rapid spread [5,6,7,8,9].

It can produce numerous seeds, is competitive against crops, e.g., ruderal and segetal spp., and is adapted to surviving in a wide range of environmental conditions; as such, complete removal using solitary control methods is difficult, due to its natural tendency to tolerate herbicides, ability to grow after mechanical methods are used and viable seed production even when suppressed by cover crops [6,10,11,12,13,14,15,16]. These characteristics may lead to a substantial crop yield decrease, creating economic strain both due to harvest loss and increased costs in control attempts [17]. Under optimal conditions, the wooly cupgrass can outcompete numerous segetal and ruderal species, strongly affecting plant community dynamics and displacing those that may be easier to control [8,9,16].

Although numerous studies were carried out on different aspects of E. villosa, there are no recent comprehensive knowledge syntheses. Certain topics are also relatively outdated, making current research fragmented and old research in need of revision. The objective of our paper is to highlight available information in a clear, concise manner in order to raise awareness and provide an introduction to its study. Additionally, we will draw attention to existing knowledge gaps as well as encourage future research directions. Therefore, our overview will cover the biology, ecology and distribution of E. villosa, as well as management strategies and economic impact, followed by a review of knowledge gaps that should be addressed in the future.

2. Species Description

2.1. Anatomy and Development

E. villosa presents adventitious roots with a dark red tough cortex [13]. Roots can also emerge from the nodes of decumbent stems as well as from the lower nodes of erect stems. Stems are 2–5 mm wide at the base and primarily grow erect, often forming tufts or clumps [13,14].

The main stem typically reaches 50–100 cm in height, although specimens over 200 cm have been reported, particularly in crop fields or damp environments [13,14,16,18]. Stem internodes are hollow and generally smooth, though fine hairs may be present near the base, followed by nodes that are densely covered with fine hairs [13]. Branching occurs throughout nodes from interposing meristems starting with the second to fourth nodes. These branches produce terminal inflorescences, which contribute to the plant’s total seed production [13,18]. Tillers are produced as soon as the third leaf stage is reached and, depending on environmental factors and germination periods, more than 10 tillers are very likely to develop; it also has the capacity to propagate via stolons [13,19,20,21,22]. Later planting causes fewer tillers to develop. In drier soils outside its preferred habitats, surviving individuals are often shorter, typically under 50 cm, and develop numerous branches that form thick clumps [16].

It presents open leaf sheaths with fine hairs and a rounded appearance [13]. It has stiff trichomes near the auricle-less apex. Ligules are 0.5 to 2 mm long, with a very short, membranous base and a hairy apex. Leaves are typically erect, up to 25 cm long and 2 cm wide, with fine trichomes on the adaxial surface and a more glabrous abaxial surface. Lower leaf edges are undulated. Main stem ends and their branches produce erect, hairy paniculate inflorescences, sized from 3 up to 20 cm in length and 1 to 3 cm wide (Figure 1a) [13,22].

The rachis is 2 to 7 cm long and generally rounded, presenting 2 to 8 branches that each hold 2 rows of 11 to 24 spikelets [13]. The spikelet pedicels are from 0.5 to 1–2 mm long, flattened and triangular and present fine hairs, along with longer bristles. Spikelets are 3.9 to 6.5 mm long and 2 to 3 mm wide with an ovate–elliptic, dorsiventrally compressed shape and mostly glabrous. The spikelet structure is quite typical for the Paniceae tribe: sterile lower floret and fertile upper floret (3.8 to 6 mm long), with the difference that the callus presents a cup-like form. The callus develops from the lower rachilla internode and first glume and presents longitudinal ridges at maturity. The first glume is rudimentary and the upper glume and sterile lemma are similarly sized, around 4.4 mm, thin, also ovate–elliptic and mostly glabrous, with seven and five thin veins, respectively. The fertile palea encloses three stamens with short, 0.5 to 0.7 mm long anthers, and has translucent margins and two thin veins. The caryopsis is almost spherical, 3 to 4 mm long and has 2n = 54 chromosomes, with 6 sets of chromosomes (x = 9; hexaploidy). The entire spikelet is a dispersal unit, with the abscission zone being right below the callus, and mature colors are greenish tan to tan and mottled purple (Figure 1b). Seedlings are very finely hairy throughout and present wider lower leaves compared to other grass species, ovate and oblong shapes, with usually red-tinged lower sheaths.

Early-season inflorescences grow on the main stem and branches, uncovered by leaf sheaths, while later-season inflorescences are more numerous, with fewer seeds, and may be partially covered by leaf sheaths. Depending on emergence timing, plant weight can vary, with later season individuals weighing less and producing fewer tillers, inflorescences and seeds [13]. Greenhouse grown individuals begin senescence during the late season even with supplemental lighting; new shoots continued to emerge densely from lower nodes after the main stem is senescent.

2.2. Physiology

2.2.1. Environmental Requirements

As a (meso)hygrophilous sp., E. villosa thrives on moist soils, such as podzols near water sources [16,18]. It is considered thermophilic due to its biological traits and distribution, but can tolerate a wide range of temperatures (Figure 2) [13]. However, prolonged droughts severely affect survival chances, with individuals in fast-drying environments unable to survive for long [16]. If winter temperatures remain above freezing and plants survive frosting, they may become facultative perennials [14,23]. When grown under high levels of photosynthetically active radiation, its dry weight increases [24]. Growth response to nitrogen is reduced in low-light conditions, indicating that it thrives in well-lit environments. In shade, leaf expansion is prioritized to increase light absorption, resulting in a nearly double leaf area per unit of biomass compared to high-light conditions. It is reported to readily grow on loamy soils with a pH range of 5.5 to 8 and an organic matter content of 2.4 to 5.8% [13]. It is sensitive to nutrient deficiency, as growth rate is reduced in nutrient-poor soils, but exhibits rapid growth under optimal conditions [24].

2.2.2. Reproduction and Germination

Flowers are bisexual, fully cleistogamous and self-pollinating [13]. Anthers are never exerted and remain attached to stigmas, with no stamens present. Flowering and fruiting periods span over several months, generally from June through September, although exact timings depend on climatic conditions [4,13].

When grown under optimal conditions, large amounts of seeds are produced, with up to 164,000 reported [20]. Sufficient water is necessary for seed production, although another important factor is the planting date, which affects the number of tillers and thus, the total seed production [20,25]. The after-ripening dormancy period is a complex enzymatic and biochemical process essential for many plants to achieve full germinative potential. Germination rates for E. villosa are below 25% immediately after harvest or before the first winter passes, as a period of dormancy of at least 6 weeks is needed [20,26,27]. First-year field emergence reached high ratesbetween 40 and 69%, higher than other problematic spp. such as Setaria faberi Herrm., Abutilon theophrasti Medik. and Amaranthus rudis Sauer., although it declined in subsequent years [28].

Oxygen plays an important role in seed germination, with total deprivation inhibiting it completely and its presence leading to an increase, with the maximum germination rate potential being reached at atmospheric levels of 16% [20]. Lower levels of 8% slowed down the germination rate by 2 to 4 days. Germination also requires relatively high temperatures, beginning around 10 °C, with a moderate increase up to 20 °C and a greater increase up to 30 °C. Rates decline moderately from 30 °C to 40 °C and cease above 45 °C [20,29]. High thermal time constants may prevent early-spring germination, reducing frost risk. Below the threshold, larger seeds show slightly better germination rates than smaller ones [29,30].

Soil moisture is more relevant compared to temperature in germination onset in spring [17]. Burial depth also influences germination rates. Higher germination is reported in superficially buried seeds [20,26]. A decrease in germination starting with burial depths of 6 cm or more was observed, with seeds near the surface requiring less energy for emergence [21]. Seed coat permeability to oxygen may be influenced by soil abrasions and add a layer of variability [26,31]. Burial depth also affected tiller production 15 days after planting, with seeds closer to the surface producing more tillers and shoot dry weight decreasing with deeper burial. Two weeks post-emergence, seeds buried at 3 cm remained more vigorous, while those at 9 cm had fewer tillers [21]. Most tillers appeared after endosperm depletion.

Seed endosperm weight declines rapidly until day 6 after germination and is depleted by day 10, with faster depletion under light exposure after day 3, especially when seedlings are grown in light with Hoagland solution, which provides essential nutrients [21]. Shoot and root growth were significantly higher in a nutrient solution compared to light or dark treatments with water alone, though light remained critical for weight increase. Development was slower in dark conditions due to endosperm reliance on nutrients. Even though light affects the germinative process after initiation, there is little to no effect on its onset [20].

2.3. Biochemical Properties

E. villosa uses the C4 photosynthetic type [29,32]. The Eriochloa genus, unlike other Poaceae, uses the phosphoenolpyruvate carboxylase enzyme (PEP), which plays a role in stomatal opening, pH regulation and the anaplerotic metabolism [32,33]. This enables a more efficient metabolism in warmer climates [13].

Allelopathic properties were detected and tested against several crops, with relevant results, showing that extracts of whole plants or even parts have a visible effect upon their germination and development [3,34].

These properties may be attributed to the presence of benzoxazinoid compounds presence. Two were discovered in 10-week-old E. villosa: DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), a hydroxamic acid and HMBOA (2-hydroxy-7-methoxy-1,4-benzoxazin-3-one), a lactam (Figure 3) [35]. Roots show no differences in quantity, but leaves contain higher amounts of HMBOA. These two compounds contribute to its development by forming complexes using metal ions absorbed from the soil. They are believed to aid in coping with harsher environments that may cause biotic and abiotic stress, such as extreme weather conditions, pests and diseases. The two benzoxazinoids produced are exuded into the rhizosphere, strongly affecting competitors by influencing their germination rate and growth [36].

The phytopharmaceutical effects of E. villosa were also studied in two instances. In one, four compounds were discovered in its extracts (chlorogenic acid, orientin, vitexin and dihydroactinidiolide) and investigated in the treatment of benign prostatic hyperplasia (BPH) in mammals, specifically rats, in upon which it induced testosterone induced (Figure 4) [37]. Prostatic weight in the E. villosa extract treatment group was alleviated, although not as much as in the finasteride group. Its effect on testosterone and DHT (dihidrotestosterone) levels was also studied as these are critical mediators of BPH pathogenesis critical mediators [38]. DHT levels were lower in the E. villosa extract treatment group, even when compared to the group treated with finasteride. Testosterone levels were lower in the E. villosa extract treatment group, although levels were higher than in the finasteride treatment group. The increase in prostatic cell proliferation was inhibited in both treatment groups, with values similar to those of the control group, thus slowing BPH progression through antiproliferative activities, reducing PCNA-positive (proliferating cell nuclear antigen) cells. E. villosa extract treatment activated the apoptotic pathway, thus reducing the amount of prostatic tissue, improving the balance between proliferation and apoptosis in BPH rats. The number of inflammatory cells was similar between treatment and control groups, with IL-6, IL-8 (interleukin), and COX-2 (cyclooxygenase) expression being noticeably reduced in treatment groups. E. villosa also aids in BPH prevention by reducing oxidative stress through the antioxidative signaling pathway. Androgen signaling in prostatic cancer cells is suppressed by E. villosa extract treatments as well. In another study that screened 75 plant spp. to identify potential candidates for anti-obesity medicine to aid the treatment of high-fat diets, E. villosa demonstrated the highest inhibitory effect on pancreatic lipases, with an inhibition rate of 83%, suggesting potential as a foundation for new anti-obesity treatments [39].

Its potential in phytoremediation was also studied. A study revealed its potential for phytoremediation of water contaminated with PFASs (perfluoroalkyl substances) [40]. Root uptake of PFASs followed the trend of river pollution levels, with plants from more polluted sampling sites containing higher levels of contaminants. Root uptake of E. villosa was compared with that of another rooted plant, Alternanthera sessilis (L.) R. Br. ex DC., and it was found that E. villosa contained higher amounts of contaminants. The authors hypothesized that its adventitious root system provided a more efficient uptake. Additionally, more of the long-chained contaminants remained in the roots compared to the short-chained ones, likely due to differences in mobility, which hindered their translocation to shoots.

3. Ecology

3.1. Habitats

E. villosa is reported to prefer agricultural land, although it is observed and often expected to spread beyond it [13,16]. It often grows beside rice fields in its native range and flax (Linum usitatissimum L.), clover (Trifolium spp.), soybean (Glycine max (L.) Merr.), sunflower (Helianthus annuus L.), corn (Zea mays L.), pumpkin (Cucurbita maxima Duchesne; Cucurbita pepo L.), sugar beet (Beta vulgaris L.), and even sorghum (Sorghum bicolor (L.) Moench) fields in invaded territories [18,22]. It is not often encountered near monoculture cereal crop fields, as they are generally harvested before E. villosa produces viable seeds, or possibly because cereal sowing density is higher [16].

It is less commonly observed in natural pastures [14], but may be more commonly found along railroads, roadsides, neglected paths, lawns, near houses, disturbed wetlands and floodplains [16,41,42,43,44,45]. In natural environments, it thrives in water-rich areas such as river sides and wet meadows, but can be found in grasslands and other areas as well [13,18,46,47].

3.2. Invasion Mechanisms

E. villosa presents impressive ecological plasticity that enables it to survive even in unsuitable environments. Individual plants may produce between 3000 and 164,000 seeds, thus ensuring a good chance of survival for next generations by increasing seedbank reserves [20]. Even in herbicide treated fields, seeds produced by surviving plants ensure the continuation of future generations, especially if only pre-emergent herbicides are applied [48,49,50]. After a period of dormancy, seeds have a high germinative rate and ability to germinate throughout the growing season after an initial main wave, as well as retain their germinative properties for over 8 years [9,13,27]. One single seed is enough to start a new population, due to its cleistogamous nature, and self-pollination ensures rapid spread even within small populations [13]. Artificial vectors play an important role in seed dispersal, and seeds’ ability to thrive in different environmental conditions means they easily colonize and settle in new areas, especially agricultural or disturbed land [14,16].

Its fast development and recovery from injury by producing numerous tillers and allelopathic chemicals provides an advantage over ruderal competitors, which leads to a tendency to dominate in certain plant communities, including crop fields [3,51]. No special seed dispersal mechanisms exist, but it covers relatively large areas around the main stem due to the production of multiple tillers and branches, each with the capacity to grow stolons early on in their development [13]. Consequently, removal is difficult by mechanical means alone, as cutting the main stem does not often kill it.

3.3. Impact on Crop Development

Among the most important competition and survival adaptations that allow a plant species to thrive in new communities is biochemical suppression and several studies were performed in order to evaluate the effect of E. villosa extracts on certain crops.

E. villosa presence was shown to lead to a decrease in certain types of chlorophyll content and photosynthetic pigments in corn, with the biggest impact on chlorophyll-A and carotenoids, with low differences in Chlorophyll-B contents [51]. A 19% to 20% reduction in relative chlorophyll content in leaves was observed at 14 and 21 days after sowing, respectively, compared to the control group. Crop development was stunted as well, with a reduction in height of 25% and 22% at 14 and 21 days after sowing, respectively, and a reduction in overall root growth, but no effect on stems. Dry weight was reduced compared to the control, by 51% for shoots and 31% for roots. Corn biochemical processes in response to competition against E. villosa were also studied. Malondialdehyde (MDA) content in corn was measured, revealing a higher level, especially in the shoots. Ascorbate peroxidase (APX), superoxide dismutase (SOD) and peroxidase (POD) activity levels were also studied. For APX and SOD, differences were only detected in shoots, while POD activities were higher in both roots and shoots, although more intense in the root of corn. Protein contents were analyzed, and the results showed that both roots and shoots contained lower amounts of proteins, with less in the roots.

The allelopathic effect of stem and leaf extracts on wild mustard (Rhamphospermum arvense, syns. Sinapis arvensis (L.) Andrz. Ex Besser) germination and development was studied [34]. Germination was not strongly influenced, with less than 15% of wild mustard seeds being inhibited by a 10% concentration solution. Germinated wild mustard seedlings were significantly affected though, as both shoots and roots were 85% shorter than the control with a 10% concentration solution. Interestingly, a 1% concentration solution had a bigger effect on development compared to 5%. Garden cress (Lepidium sativum L.) is also susceptible to E. villosa extracts [52]. To test the germination rates of garden cress with extracts, 4 and 8 g/100 mL stem and leaf extracts were prepared. Stem extracts suppressed germination by an average of 35% when exposed to the 4 g/100 mL extract and slightly lower for the 8 g/100 mL extract. Leaf extracts were less potent, with the germination of the garden cress under the effect of the 4 g/100 mL extract being on average 60%; the 8 g/100 mL extract had a stronger effect, with the germination rate being below 50% in all cases.

Germination rates of sunflower, lettuce (Lactuca sativa L.) and white mustard (Sinapis alba L.) seeds were measured when exposed to different concentrations of E. villosa sprout, root, and spiculum extracts [3]. On sunflower germination, 4% concentration root and sprout concentration extracts had some effect, while spiculum extracts had none. Sprout extracts of 8% concentration sprout extracts had stronger inhibitory effects against sunflower germination compared to either root or spiculum extracts. On lettuce seed germination, 4% root and sprout extract effects were notable, with the spiculum one less potent. Extracts of 8% concentration extracts showed similar results. Corn germination exhibited the most tolerance against E. villosa extracts, with very low effects regardless of the extracted part or concentration. On white mustard germination, root extracts were inhibitory for the at largest tested concentration, 10%, although the most pronounced effect was that of the sprout extract, with both 5% and 10% concentrations almost halting germination altogether.

3.4. Plant Community Dynamics

E. villosa is generally detected on agricultural and disturbed areas more than in natural areas, although when it does reach such areas, it may become dominant under the right environmental conditions [16]. In Romania, a study revealed its tendency to associate with other dominant Poaceae spp. such as Setaria pumila (Poir.) Roem. & Schult. and to a lower extent Panicum miliaceum L. and Echinochloa crus-galli (L.) P.Beauv. [16]. E. villosa is believed to be part of the Stellarietea mediae class of synanthropic annual plant spp. [9]. In a study on transplantation date and integrated weed control in a field of aromatic black rice (Oriza sativa L.) in India, E. villosa was one of the most dominant overall and the most dominant among other grassy weeds [8].

3.5. Other Biotic Influences

Like many other weed spp., E. villosa may be susceptible to agricultural pathogens, which turns it into a disease vector [13,53,54]. Even so, only a few studies have been undertaken on this.

Fusarium culmorum (Wm.G.Sm.) Sacc. (1892), an important fungal pathogen causing root and kernel damage in wheat that leads to yield reductions, was recently isolated from E. villosa, although no signs of disease were detected yet [55,56,57]. Because the fungus was detected in the rhizosphere, an endophytic relationship is hypothesized.

E. villosa is a potential vector for Clavibacter nebraskensis, a Gram-positive bacterium, as lesions and bacterial streaming were observed on its leaves [58]. This microorganism causes Goss’s leaf blight and wilt in corn, which may lead to significant yield loss.

A Paris-type mycorrhizal infection was detected in E. villosa, in China [59]. These structures were present in the cortical cells of roots. While specific interactions between the two species were not studied in detail, these types of structures are generally symbiotic.

Animals also feed on E. villosa seeds, with invertebrates such as beetles and crickets, as highlighted in a study of seed predation in Canada [60]. Birds and other vertebrates also fed on its seeds.

4. Distribution and Spread

4.1. Native and Invasive Range

E. villosa is native to several Eastern Asian countries such as China, Japan, North and South Korea, Vietnam and part of Russia [1,4,7,15,61]. It is considered a neophyte in other territories, as the first official report outside its native range was in the 1940s in the USA where in time, it established itself in many of the Midwestern states. The first official record of its presence in the US was in Oregon and Colorado, in 1950 [62]. It has now been confirmed in Ohio, California, Illinois, Iowa, Kansas, Minnesota, Missouri, Mississippi, Nebraska, Pennsylvania, Wisconsin, Florida and California [41,63,64]. An alarm was raised beginning in the 1970s due to its spreading speed and persistence [26]. Eventually, it also reached Canada, where it was detected for the first time in 2000, near Quebec [13,25].

Although native in far eastern Russia, it is considered invasive in other territories [1,65]. Official reports were made in the European Russian territory (Saratov, Voronezh, Belgorod and Samara provinces), with Altai and Tomsk recently being recently considered to be the main settlement centers of E. villosa populations, where they occupy both cropland and ruderal areas [9,47,65,66,67].

There are few mentions in Ukraine, with the first being published in an identification manual of the country’s vascular plants [68].

In Romania it was first reported in 2006, in the north of the country, in Satu Mare county [18]. It is possible by the first observation’s location that it spread here from the southern Ukrainian territories, although just one year later, it was reported in Banat County (Timiș and Caraș-Severin) so artificial means of introduction are also possible [22]. Established populations were also reported in numerous North-Western Romanian counties such as Bihor, Sălaj and Arad [7,16,18,69,70,71]. It was also detected in the center of the country, in Alba and Dâmbovița County [2,71]. While published works show Timiș County as the area with the most stable populations of E. villosa, it is presumed to be much more widespread in reality and that most populations have simply not yet been officially reported, which may be the case for other countries as well [16].

The first record of E. villosa in Hungary was in 2008 [72]. In Hajdú-Bihar County, it was reported in 2011, and in Somogy county in 2013 [73,74]. Further studies also confirmed its presence in other areas such as Trans-Tisza Region [75]. While it is a continuously spreading sp. often considered problematic, the number of studies in Hungary is still minimal [3].

In the Czech Republic, it was first reported in 2014 near the Austrian border, where it is assumed to have been brought over by means of agricultural activities using machines, as reported in 2020 [7,76].

Works from other European countries sometimes mention E. villosa. It was included in a list of alien grasses in the British Isles in a 1999 flora atlas as a dock alien, described in a guide of herbaceous plant spp. in Denmark in 2014 [77,78]. Its presence was also reported in atlases in Belgium in 2017 and France in 1992, where it is now more commonly detected [23,79,80].

According to the Global Register of Introduced and Invasive Species (GBIF), there were reported occurrences in Poland and Sweden as well [61].

E. villosa is a continuously spreading weed species, with new reports of its presence increasing in recent years, as presented in Figure 5.

4.2. Introduction and Spread

E. villosa has notable ecological adaptations, and thus can easily establish itself in new areas, especially disturbed fields or plots of fallow land [16,22]. One of the leading causes of involuntary human aided artificial spread is its synanthropic tendencies. Agricultural machines are notable vectors of spread between neighboring fields, as seeds can be found within residues of stalks and leaves that resulted from sifting in combine harvesters [3,74]. On a larger scale, railways and roads may also act as a conduit of dissemination for E. villosa, as there were several reported instances in which it was found along train tracks and along roads that connected an area with an established population and a newly colonized area, surviving and spreading even in gravel [22,41]. Interestingly, there is a record of E. villosa as an ornamental grass cultivated in certain areas [65]. International seed trade is another common introduction method way in new countries and should be extensively monitored [2,16,22,45].

Certain wild birds feed on E. villosa seeds and may act as disseminators, although collared doves fully digest seeds, none of which are viable after passing through their digestive tract [3]. Field voles (Mus agrestis L.) are also known to consume E. villosa seeds, but the spread would most likely be minimal due to their small size and movement limitations [3].

5. Management Strategies

A large part of the Western scientific publications with the objective of testing herbicidal chemical control against E. villosa were published between 1980 and 2000, many in the United States. It is considered problematic in its native range as well, and later publications were often conducted in Asia, especially China, using newer compounds.

Usage of more than half of the active ingredients tested within that time period is now banned in the European Union due to their negative impacts on against the environment, which led to fewer known effective active ingredients that may be used against E. villosa.

Controlling E. villosa in monocotyledonous crop fields is challenging due to crop susceptibility to stronger selective herbicides. It is especially difficult to control in corn due to it being a row crop, as with sufficient space and light, it will enable E. villosa to thrive in the available space.

Each control method presents certain advantages and disadvantages, but using integrated control methods is generally considered to be the fastest and safest way to control invasive species, including E. villosa. Ideally, control should be achievable within 2 years of adopting proper integrated control methods [22].

5.1. Chemical Control

Weed chemical control became one of the most efficient and widespread control methods as it requires less workforce and is relatively cheap, quick, and easy to use and sowing herbicide-resistant crop hybrids also opens the possibility of using a larger range of products on previously incompatible crops. Herbicidal compounds can vary greatly in composition, type of action against plants and targeted processes or organs, which led to classification attempts being made by various institutions and organizations. Widely accepted ones are the HRAC (Herbicide Resistance Action Committee) and WSSA (Weed Science Society of America), based on their mode of action [81]. Currently approved herbicides that have been tested against E. villosa will be discussed in order of their HRAC classifications, followed by their chemical families. Currently, the European Union has one of the shortest lists of approved herbicides and this will be used as reference in our paper. Even so, very few have been tested in their efficacy against the E. villosa. (Figure 6).

Due to the increasing usage of herbicides worldwide and their associated negative environmental and health impacts, this review prioritizes discussing active ingredients that are currently approved for use in the European Union as of 2025 [82,83]. The focus on European legislations allows us to present lower-toxicity substances regulated by rigorous and strict environmental legislations in order to encourage sustainable herbicide and pesticide practices.

5.1.1. Group 1—Lipid Synthesis Inhibitors

This group contains compounds that inhibit acetyl coenzyme A carboxylase (ACCase), with an important role in the fatty acid biosynthesis pathway. They halt cellular growth due to their effect on lipidic membranes, which lead the plant to wilt and eventually die.

Clethodim belongs to the hydroxyoxocyclohexenecarbaldehydeoxime chemical family. It is selective towards grasses and can be applied to broadleaf crops. It is used in post-emergence-foliar herbicide formulations. E. villosa can be successfully controlled by a clethodim based herbicide applied at 240 g/L EC (90 g A.I./ha), if an individual plant has two or fewer leaves [84]. It is also reported that clethodim has a “certain control effect” [85].

The following four herbicides are all part of the hydroxyphenoxyisopropionic acid chemical family:

Fenoxaprop-P-ethyl is selective towards both annual and perennial grasses, especially before tillering. While it can be applied to monocotyledonous crops, a safener is required to prevent any potential damage. It is used in post-emergence foliar herbicide formulations. Once absorbed, it is quickly hydrolysed, converting into an acid that stunts growth and causes chlorosis, necrosis, and eventually death. In a pot trial, Fenoxaprop-P-ethyl (69 g/L EW, applied with 3%/5% safener at 57 g/hm²) provided excellent control of E. villosa, with 100% control 30 days after application [86].

Fluazifop-P-butyl is mostly selective towards annual grasses, although it can also control several perennials. Herbicide formulations based on it are applied as foliar, post-emergence treatments. Growth is halted two days after application; growing points undergo necrosis and young leaves develop chlorosis, although mature leaves may retain their vigor for a while longer [87]. However, plants generally die within 3–4 weeks of application. It can control E. villosa before it reaches a two-leaf growth stage at 15% EC, applied at 135 g ai/ha [84].

Both quizalofop-P-ethyl and quizalofop-P-tefuryl are used mainly against grasses, although they are not highly selective and may affect non-target grasses. Herbicides based on either of them are applied as post-emergence treatments, during the active growing phases of the target. Quizalofop-P-ethyl is able to control E. villosa before the two-leaf stage is reached when applied at 5% EC, at 71.25 g ai/ha, similarly to quizalofop-P-tefuryl, at 40 g/L EC and 36 g ai/ha [84,86].

5.1.2. Group 2—ALS Inhibitors

They inhibit the acetolactate synthase enzyme, with a role in branched amino acid biosynthesis, halting the production of valine, leucine and isoleucine [88].

The herbicides discussed in this subchapter are part of the sulfonylurea chemical family.

Nicosulfuron may control both annual grasses and several perennials. Given that Nicosulfuron is a widely used herbicide, E. villosa’s susceptibility to it was tested. It is tolerant to reduced Nicosulfuron rates, with individuals requiring over 72 h to metabolize 50% of the herbicide [89,90]. In Liaoning province, China, four populations were found to be highly resistant, while 11 populations were moderately resistant, 13 were minimally resistant, and only 1 population was susceptible to Nicosulfuron [91]. Resistance was correlated with an increased GST (glutathione S-transferase) activity in resistant populations. Another study revealed that ALS and chlorophyll recoveries were faster in resistant populations [92]. Published results of Nicosulfuron efficacy experiments are relatively old and show varying outcomes depending on populations, area, weather, and dosage. Nicosulfuron applied in one or two sequential treatments at different rates provided good to excellent control over two years of experiments [49]. Single treatments applied at 34, 56, and 67 g/ha had efficacies of 87%, 92%, and 91%, respectively, 85 days after treatment. The following year, treatment rates resulted in efficacies of 92%, 94%, and 96%, respectively, at 104 days after treatment. Sequential Nicosulfuron treatments (early post- and post-emergence) yielded slightly better results when applied in combination mixes of 22 g/ha and 34 g/ha each. At the five- to seven-leaf stage, Nicosulfuron applied at different rates showed good control of E. villosa 8 weeks after application, with efficacies of 70% (18 g/ha), 77% (27 g/ha), and 85% (36 g/ha) [5]. Nicosulfuron applied alone at 35 g/ha provided fair to good control 60 days after treatment, with efficacies of 60%, 82%, and 83% over three years. Depending on the application year’s weather conditions, plant density reduction ranged from 47% to 63% [50].

Foramsulfuron is selective towards certain annual grasses, while leaving others unaffected. Herbicides based on it are applied as post-emergence treatments. Depending on the adjuvants, E. villosa readily absorbs it, with absorption rates ranging from 34% to 81% [93]. Although absorption rates are relatively high, Foramsulfuron tolerance is substantial. Field and pot trials yielded unsatisfactory results in terms of control, with efficacy values ranging from 5% to 20% at a 37 g/ha application rate. The low sensitivity of the ALS enzyme, low translocation rate (with the substance mostly remaining in the leaves), and rapid metabolism are suggested possible explanations.

Halosulfuron-methyl is primarily selective towards sedges [87]. It is applied once or twice per year, post-emergence, on young, actively growing weeds. Symptoms may take several weeks to develop [94]. It was used in combination with sethoxydim, a banned herbicide, against E. villosa [50]. Control was slightly better compared to sethoxydim applied alone, with control rates ranging from 87% to 97% at 60 days after application.

Prosulfuron has low selectivity, as it targets a relatively wide range of weeds. It should be noted that while prosulfuron has been tested against E. villosa, it was part of a combination of three herbicides that yielded good results [50]. The other two herbicides are no longer approved, but testing prosulfuron in future experiments may be a viable option.

5.1.3. Group 3—Microtubule Inhibitors

They disrupt the mitotic process by binding to tubulin and inhibiting microtubule polymerization, which prevents the proper formation of spindles by disrupting the correct separation and alignment of chromosomes [95]. They are typically included in broad-spectrum herbicides that are applied as pre-emergence treatments [96].

Pendimethalin belongs to the dinitroaniline chemical family. It is used in broad spectrum pre-emergence herbicides that inhibit root and shoot cell division in young plants and seedlings [96]. While there are no recent studies on its effectiveness against E. villosa, past studies show that it provides acceptable to good control, especially when combined with other pre- or post-emergence herbicides [11,49,97,98]. It is reported as a poor post-emergence treatment. While many of the other active ingredients it was tested with are no longer approved for use in the European Union, pendimethalin remains a viable option as of 2025. Certain combinations may lead to crop injury, so it is recommended that combinations be made carefully to avoid long lasting damage [99]. It is also important to consider environmental conditions and application timings to achieve favorable results [48].

5.1.4. Group 5—Photosystem II Inhibitors

By binding to the D1 protein within the photosystem II complex, they prevent electron transfers and disrupt photosynthesis. The following production of reactive oxygen species causes cell damage and leads to death [100].

Two active ingredients are discussed in this subchapter, both part of the triazinone chemical family.

Metribuzin is used in broad-spectrum herbicides. These can be applied both pre- and post-emergence [101]. It is easily absorbed by roots and seedlings, as well as by leaves. When applied alone against E. villosa during pre-emergence, a metribuzin-based herbicide (600 g/L at 1 L/ha) did not efficiently reduce its biomass, achieving only 20% efficacy 30 days after application. However, when combined with s-metolachlor, results were much better, reaching 84% efficacy [47].

Terbuthylazine is used in broad-spectrum herbicides. It is applied both pre- and post-emergence, generally against broadleaf weeds, although it is also effective against some grasses [102]. In the herbicide formulation it was part of, s-metolachlor (312.5 g/L) and terbuthylazine (187.5 g/L) achieved 56% efficacy against E. villosa when applied at 4.5 L/ha [47]. It is important to note that s-metolachlor has not been approved for use starting with 2024.

5.1.5. Group 9—EPSP Synthase Inhibitors

5-enolpyruvylshikimate-3-phosphate synthase is important in phenylalanine, tyrosine, and tryptophan synthesis via the shikimic acid pathway, and inhibitors of this enzyme lead to deficiencies that affect protein and hormone production, causing the plants to wilt and eventually die [103,104].

Glyphosate is part of the phosphonomethylglycine chemical family. It is mostly used in broad-spectrum herbicides, although it can also be used as a desiccant under certain conditions. It is applied post-emergence, as it has no effect on germination. Fields of glyphosate-tolerant soybeans containing E. villosa are often treated with glyphosate, making it a viable control option.

Applications during the soybean flowering stage (R1) are synchronized to the beginning of E. villosa flower fertilization. The effect of glyphosate on seed viability before inflorescence emergence, during post-anthesis, was studied [15]. There were almost no differences between the 900 g a.e./ha and 1800 g a.e./ha treatments regarding seed abortion, which was minimal. Seed weight differed between treatments, with 0.8 g for the control, 0.4 g for the 900 g a.e./ha treatment, and 0.2 g for the 1800 g a.e./ha treatment. Treated plants often produced seeds with immature or missing caryopses, with only 4% viable seeds after the 900 g a.e./ha treatment and 0% viability after the 1800 g a.e./ha treatment. Although application at this timing may not increase crop yield, it can significantly reduce E. villosa seed viability, leading to a reduced seed bank and slower spread. While the plants are highly sensitive to glyphosate and no tolerant populations have been discovered so far, it is suspected that they may eventually become resistant [105].

5.1.6. Group 13—DOXP Synthase Inhibitors

1-deoxy-d-xyulose-5-phosphate synthase inhibitors affect the biosynthesis of carotenoid pigments, which leads to the destruction of chlorophyll. Once applied, foliage becomes bleached, and affected plants eventually die [96].

Clomazone is part of the isoxazolidinone chemical family. It is a broad-spectrum herbicidal substance that can be applied both pre- and post-emergence. In a formulation of 480 g/L at 1 L/ha, clomazone tested in vegetation experiments achieved poor results, with only 28% efficacy against E. villosa [47].

5.1.7. Group 14—PPO Inhibitors

Protoporphyrinogen oxidase inhibitors, also known as membrane disruptors, are compounds that inhibit the PPO enzyme that plays a role in chlorophyll catalysis and heme biosynthesis [98]. When cell membranes are disrupted, rapid chlorosis and necrosis ensue due to peroxidative agents’ accumulation [106].

Flumioxazin is part of the N-phenyl-imides chemical family. It can be applied both pre- and post-emergence, and although it is generally considered more effective against broadleaf weeds, it can also control certain grasses [107]. When tested against E. villosa in a formulation containing 50% active ingredient applied at 0.12 l/ha, the treatment had almost no effect against it, with a control rate of 2% [47].

5.1.8. Group 15—Long-Chain Fatty Acid Inhibitors

VLCFA inhibitors that reduce plant growth, thus severely limiting lipid and protein production [108].

Dimethenamid-P is part of the chloroacetamide chemical family. It is selective towards grasses, including some notoriously hard-to-control weeds such as Sorghum halepense. Herbicides containing dimethenamid-P are generally applied as pre-plant-incorporated, pre-emergence, or early post-emergence treatments. Control of E. villosa was mostly tested in combinations, either in mixes or through multiple applications. Due to environmental moisture and rainfall dependency after application, results varied and were generally inconsistent [5,49,50].

5.1.9. Mentions

We will briefly mention of herbicides that were tested with varying degrees of success but are no longer in use in Europe. These could still be relevant in the search for effective approved herbicides, as understanding their mode of action and chemical class may help in choosing the best alternatives to test.

Tested and now-banned herbicides are the following: Acetochlor, Alachlor, Ametryn, Atrazine, Bromoxynil, Butylate, Cyanazine, Cycloate, EPTC, Glufosinate, Haloxyfop-P-methyl, Haloxyfop-R-methyl, Imazethapyr, Linuron, Metolachlor, Primisulfuron, Prometryne, Propachlor, Propisochlor, Pyroxasulfone, S-metolachlor, Sethoxydim, and Simazine [5,10,11,12,47,48,49,50,83,84,85,98,109,110,111,112,113].

Although several herbicides may be highly effective against an initial wave of E. villosa individuals, its ability to germinate throughout the season requires a treatment program involving two or more applications for full control, as most post-emergence herbicides dissipate after a short period of time [6,12,13,15]. Pre-emergence, soil applied herbicides are not very effective against E. villosa either [12]. Excessive herbicide use is becoming a growing concern, as populations are increasingly tolerant. Zero till fields are disadvantageous because they require more frequent herbicide applications to maintain control, which can contribute to an increased tolerance of E. villosa [15,114].

5.1.10. Conclusions to Chemical Control Research

Despite increasing efforts to discern the best treatments against E. villosa, certain active ingredients have proven to be completely inefficient, while others have provided promising results, especially when applied as indicated by the product labels they are a part of. Some of the most efficient herbicidal substances are currently post-emergence herbicides that are part of Group 1 (lipid synthesis inhibitors): clethodim, fenoxaprop-P-ethyl, fluazifop-P-butyl, quizalofop-P-ethyl and quizalofop-P-tefuryl, although their efficiency depends on early applications, on individuals with no more than three leaves. Group 2 (ALS inhibitors) contains Nicosulfuron, an extensively researched herbicide against E. villosa with contrasting results depending on application timings and environmental conditions, although the consensus is that it is especially highly efficient against young seedlings. Group 9 (EPSP synthase inhibitors) contains glyphosate, which is recommended against this species in tolerant soybean fields during post-anthesis of E. villosa individuals, as it significantly reduces seed numbers. It is also important to note that not all herbicides mentioned in this review are compatible with all crop species and a careful choice regarding the best product for each crop is advised. As an honorable mention, out of the now banned in European active ingredients, sethoxydim was successfully used against E. villosa with great results.

5.2. Mechanical Control

Mechanical control involves physical removal or disruption of weeds from fields or disturbed soils, either through manual labor on a small scale or with machinery on a larger scale. One of the oldest weed control methods, dating back to prehistoric times, it remains an essential component of integrated weed management and is still widely used today [115].

Tilling is an effective method for the removal of aerial parts of weed individuals and weed seed bank reduction over time. However, it does not always ensure complete root destruction, particularly when weeds have developed resistant perennial forms [116,117]. To give crops a better chance at early development, it is recommended to sow immediately after the final tillage, before weed seeds have an opportunity to germinate first [22]. Infested fields should be harvested and tilled last to prevent seed contamination between fields via machinery [22]. Excessive tilling can lead to soil degradation, although zero-till fields also have drawbacks, including increased herbicide use needs, which may promote E. villosa to develop tolerances against the most commonly used herbicidal compounds [15,114,118,119].

Crop field cultivation was one of the main weed control methods before herbicide development, and with the risks of weeds becoming tolerant following their intensive usage, it is regaining popularity [115,120].

Mechanical control of E. villosa was studied independently, as well as in combination with chemical control methods. The effects of full and half dose combinations of sequential pre-emergence and early or late post-emergence herbicide applications were studied, with or without cultivation [12]. Reduced rate herbicide applications followed by cultivation provided highly effective control, as they maximized crop yield and minimized weed seed production, thereby reducing the seed bank. Similarly, excellent results were reported when cultivation was combined with post-emergence treatments, whereas row cultivation alone yielded mediocre results, particularly when assessed later in the season [10,11].

While these studies show promising outcomes, many herbicides used at the time are no longer approved for use. Therefore, new studies using currently accepted alternatives are needed to evaluate the efficacy of this hybrid method against E. villosa specifically.

5.3. Agricultural Control

Agricultural and biological control against invasive weeds generally involves using living organisms to suppress weed development and spread, making weed management easier within sustainable, integrated control programs [121]. While herbicide amounts may be reduced, careful planning and consideration are required, as biological agents may negatively affect crops and disrupt the surrounding ecosystems, although no dedicated studies have been performed on this species so far [122]. Consequently, developing safe and effective biological control methods may end up being costly and time consuming.

Crop rotations are a historically effective biological control method in weed suppression [123]. To achieve satisfying results, crop spp. and varieties must be carefully selected, and rotations thoughtfully planned along with other control methods. Longer rotations and a variety of crops have the highest chance of providing better outcomes in both yield and weed control [124,125]. Their potential effectiveness is partly explained by field activities that disrupt weed life cycles and give dominant spp. less time to adapt to changes [126,127]. Additionally, differences in nutrient uptake among crops and variations in resource availability play crucial roles in reducing weed populations by disrupting their growth patterns [128,129].

For E. villosa, crop rotations have been recommended as part of weed control management strategies for at least 30 years [13,25].

Using only annual crops in rotations may not provide the best results, however. It is recommended that cover crops are included for more than one year to have a better chance at controlling E. villosa [13]. Cover crops that establish quickly produce high amounts of biomass, which makes them good resource competitors while also providing a great way of covering fallow fields after crop harvests, preventing weed growth and soil erosion [130,131]. Depending on the cover crop, the soil is enriched through nutrient recycling and absorption, which aids future crop development [132].

E. villosa is sensitive to nutrient and light scarcity, and depending on the chosen cover crops, its growth may be stunted and seed production reduced. A study mentions that legumes such as alfalfa or clover added to rotations as an alternative to herbicidal applications may not be enough to control it on their own, as E. villosa can emerge from unmanaged forage plots and produce seeds that easily germinate even in the absence of light [6,20]. It continues to survive and create seed-producing tillers after mowing and may go undetected within these fields until the next crop replaces them [6]. Certain spp. such as rye (Secale cereale L.) have allelopathic properties and, although its direct effect on E. villosa has not been yet studied, it is considered a better cover crop than wheat [89]. Soybeans are also effective as a rotational crop, as grass selective herbicides can be safely applied [13,22].

In conclusion, research of the agricultural control of E. villosa currently shows moderate effects of the crop cover control method alone, with dense-biomass legume species and allelopathic species showing the most promising results, although extended studies should be considered in the future for clearer results. In addition, while natural pathogens of this species exist, no dedicated studies have been performed so far, and an introduction should not be created without extensive studies to research the impact it may have on the environment.

5.4. Preventive Measures

Only managing already established populations is not enough, as new ones will likely continue to spread or be artificially introduced, highlighting the need for preventive strategies [132]. Prevention is important against E. villosa, given its accelerated spread and difficulty of its removal from non-native areas [22].

The EPPO uses Pest Risk Analysis (PRA) to assess pest risks in specific areas and recommend appropriate control measures based on each situation. PRA were first used to study invasive plants in 2002 [133]. These schemes are very thorough, making it difficult to conduct a PRA for every individual species. In response, the EPPO Prioritization Process was developed to identify spp. that pose the highest risk, determining which PRAs should be prioritized.

The Australian Weed Risk Assessment (WRA) is the first and most widely acknowledged risk assessment tool [134]. While newer tools may offer more precision, the information required to assess a species’ impact on ecosystem processes and population dynamics is often unavailable for emerging spp., making it difficult to draw definitive conclusions [132].

Another preventive strategy provides a faster risk analysis tool to assess the invasion potential of new species [132,135]. In order to achieve a highly accurate result however, a thorough understanding of already-established populations and their distribution is required, along with early detection of newly introduced or established ones. While it is relatively fast and reliable system, spp. that pose threats to biodiversity, rather than those affecting agrosystems are primarily targeted.

Ensiling is another effective preventive method against the dispersion of a wide range of weed spp. [136]. Monocotyledonous spp. seeds tend to be more susceptible to ensiling compared to dicotyledonous ones, possibly due to their smaller size and weaker protective coating [137]. The effect of ensiling E. villosa seeds in alfalfa and corn, as well as the relationship between seed viability and impermeability in experimental mini-silos, was studied [138]. They found that E. villosa seed impermeability had no correlation with seed survival in silos after one month. Although seed viability exceeded 85% before ensiling, it dropped to below 5% after just 1 month, and less than 0.1% of seeds remained viable after 3 and 6 months in both corn and alfalfa, an effect attributed to the degradation of seed coats caused by microorganisms. The authors note that herbicide-resistant spp. may exhibit different viabilities under the same conditions, but it remains highly unlikely that seeds could survive ensiling for more than 4 months, as observed in other resilient ones.

6. Economic Aspects

6.1. Awareness

E. villosa was not considered problematic when first discovered outside its native range, as its spread was slower than that of other weeds and invasive mechanisms were not fully understood at the time [14]. It was temporarily added to the EPPO (2012) Alert List in 2008, then removed in 2012 and transferred to the EPPO Observation List. It is recommended that this sp. is re-added, as multiple studies has shown that its spread is becoming increasingly concerning. A risk assessment report from France identifies it as a potential invader, with an intermediate score of 24 on the Webber and Gut [135] scale [132]. In Romania, it is known to be difficult to remove once established, making it impossible to ignore in most areas where it is found. It was compared to Ambrosia artemisiifolia L. due to its adaptability, rapid spread, and ability to colonize new areas [22].

6.2. Economic Impact

Weeds can impact the economy in various ways, including yield loss, reduced forage quality, toxicity to livestock, and increased control management costs in agriculture [139,140,141,142,143]. They also contribute to environmental changes, infrastructural damage, and in some cases, pose health risks through allergies or poisoning [144,145,146].

While E. villosa does not pose all the risks typically associated with invasive weeds, it can greatly reduce crop yields and impose substantial management costs [3,5,6,7,27,89,147]. Yield losses are closely tied to factors such as seedling density and control measure timings [17]. Effective management of E. villosa often requires sequential herbicide treatments or integrated strategies to minimize its impact on crop production [6,13,105,148].

Over the years, numerous studies have tested the effectiveness of various control methods. For example, it was found that corn yield was similar in plots treated either pre-emergence or early post-emergence, with or without row cultivation [147]. However, delaying treatment until E. villosa reached 15 cm in height often led to yield reductions. Post-emergence application to weeds up to 10 cm tall provided satisfying yields and equal or better control compared to pre-emergence treatments.

Row cultivation was also recommended as part of herbicidal spraying plans. Combining row cultivation with herbicide treatments increased yield by 11% to 28% compared to herbicide treatments alone, and row cultivation on its own provided a 103% yield improvement compared to untreated controls [11]. Delayed pre-emergence and post-emergence treatments were more effective than early post-emergence applications, although environmental conditions—such as drought, excessive moisture, or cold weather—sometimes reduced herbicide efficacy and affected crop vigor, which in turn affected yield.

Combining pre-plant incorporated (PPI) and pre-emergence or early post-emergence treatments led to higher yields compared to PPI alone [48]. The effectiveness of these timings depends on specific herbicides and the control they achieve under varying environmental conditions. Sequential herbicide applications generally outperformed pre-emergence treatments alone, and lower doses of post-emergence herbicides were as effective as full doses of pre-emergence treatments when applied alone, resulting in comparable yields [5,49].

Maximized yields were also achieved using sequential applications of full-rate pre-emergence herbicides followed by either full- or half-rate post-emergence treatments [12]. Half-rate sequential applications combined with row cultivation also delivered comparable yield outcomes, highlighting the potential of integrated management approaches to optimize crop production.

Although many studies emphasize its impact on crop yield and management difficulties, there are few that have written about its direct effect on exact costs and losses, especially on crops other than corn. In order to illustrate the reported effect of E. villosa on crop yield,

Table 1. This table represents the direct effect of E. villosa on corn yield loss, as reported in the literature by scientific researchers already cited throughout this review.

Yield Loss %	Control Yield	Best Treatment Yield	Citation
88.37	500 kg/ha	4300 kg/ha	[113]
87.31	17 bu/acre	134 bu/acre	[49]
73.29	2150 kg/ha	8050 kg/ha	[11]
72.56	2250 kg/ha	8200 kg/ha	[48]
44.21	5300 kg/ha	9500 kg/ha	[113]
38.66	7300 kg/ha	11,900 kg/ha	[5]

was created to present percentages of loss between control and the best treatments in each paper that directly presents the negative effect of E. villosa on corn. The lack of precise economic data highlights the need for further emphasis in future research to better understand the effect E. villosa has on the economy.

While E. villosa poses an increasing risk to the agricultural sector as a persistent competitor of crops, it also has several characteristics that give it the potential to become an environmentally and medicinally valuable plant.

Due to the properties of several molecules discovered in E. villosa, its medicinal potential was highlighted in several studies discussed in Section 2.3 that present its effect against benign prostatic hyperplasia and as an anti-obesity treatment. As also mentioned in Section 2.3, E. villosa has potential in phytoremediation programs due to its ability to uptake PFASs through its adventitious roots.

It is briefly mentioned that it has some nutritional value as livestock feed, as it is regarded as a poor to fair forage [13].

7. Future Directions

Numerous studies that focus on E. villosa highlight the dangers it poses to crops and several investigate its potential in medicine, but interest remains relatively new and awareness among scientists and farmers is not widespread. As a result, there are certain research gaps that, if addressed, could benefit the agricultural and medicinal sectors in the future.

E. villosa anatomy is well-documented in the scientific literature, and while variety between populations may exist, no notable phenotypical differences have been reported so far. No in-depth studies of its genetic makeup have been preformed either. Awareness of the distribution of different varieties, genotypes, and phenotypes of E. villosa would provide important information about its recent spreading history. Mapping these aspects across populations can help detect patterns and improve our understanding of its expansion over time. Searching for already-established populations is the first step in better understanding its distribution patterns. Also, identifying specific habitats and environmental conditions where E. villosa populations occur, as well as the plant community dynamics they are part of, would increase our knowledge of its chorology. Such information would enable the capacity for further analysis in order to predict its future spread.

Its biochemical processes could be further studied to develop effective control strategies by examining herbicide susceptibility and metabolism, allelochemical production and triggers, stress tolerance mechanisms, as well as nutrient uptake and photosynthetic efficiency. Additionally, such research could potentially lead to the development of potent medicines based on its molecular properties and explore its potential use in phytoremediation.

Studying E. villosa and crop interactions may help determine which are the most well-suited for resource competition the least susceptible to allelochemicals, which may lead to creating efficient crop rotation programs that have a higher chance of reducing weed seed banks and as such, future competition.

Analyzing plant community dynamics is also crucial for understanding E. villosa as it tends to dominate under optimal conditions. Its interactions with segetal and ruderal spp. provide insights into which niches it occupies. Additionally, it may pose a greater risk to agriculture by displacing easily manageable weeds and serving as a vector for disease. Similarly, its impact on spontaneous native flora could lead to biodiversity loss and alterations in soil hydrology and chemistry.

Its potential as a vector for disease and pests can be assessed when populations are discovered near crops from the same family, and it should be determined whether the diseases they carry transfer to E. villosa, especially after harvest as well as in the following years. Similarly, it could also harbor beneficial symbiotic fungi that have not yet been detected in its roots, which might aid in its competition for resources against crops and other weeds.

E. villosa control is difficult due to its characteristics and ecological plasticity, and not enough recent studies have been performed to determine which course of action is most efficient and cost-effective. There is a lack of chemical control studies using novel and more environmentally friendly substances, possibly due to its known tolerance, but studying their effect on E. villosa is important, as even if chemical control does not solely suppress populations, it may be used within integrated control programs, which is very often recommended either way. It is possible that substances that are able to suppress similar spp. might suppress E. villosa as well, although appropriate studies are needed to assess its response.

Other control methods should be studied as well, as integrated control methods are generally more efficient and environmentally friendly. Mechanical control has been studied against E. villosa, but not intensively. Tillering is efficient in combination with chemical control, although it is not possible to perform it during developmental phases unless it is used in row cultivation in crops like corn and sunflower. For road sides, train tracks and disturbed land, other methods such as multiple trimmings during the flowering phase, before seeds form and become viable, are possible Boiling plants using hot-water jets or using foam or flame guns may be another fast and efficient method to prevent its spread into new territories and reduce seed banks.

Biological control using introduced pathogens or pests is risky without knowing the full extent of their environmental impact, but knowing how they interact in laboratory and greenhouse conditions could help understand the chances that E. villosa cupgrass would have in new territories where these species already exist, and they could possibly feed on it or infect it.

It is highlighted in newer findings that it has the potential to become a valuable plant in multiple industries. Its capacity for phytoaccumulation of plastic in polluted water bodies means the plants may be able to extract other types of toxic contaminants, as well. Also, the availability of medicinally valuable molecules could lead to the production of commercially available medicine. The seed and plant’s itself values could also be of interest as fodder and pet food, as it is considered an acceptable forage for livestock.

8. Conclusions

The presented synthesized knowledge on E. villosa strives to raise awareness on the risks it poses in agriculture and biodiversity, but at the same time communicate its potential as a medicinal plant and livestock food source.

Regardless, its placement on watchlists is strongly recommended in countries where it is already established and, possibly, within the territories close to these areas, in order to raise awareness of its spread risks as much as possible. Its spread may lead to uncontrollable established populations and growing seed banks, and it warrants action from the administration and policymakers of territories, as well as awareness campaigns to inform farmers and people responsible for common roads and train tracks, along which way it often seems to spread.

Measures should be taken to determine the best control methods depending on environmental conditions, typical crops and infestation levels. For these programs to be possible, research on its response to control methods are necessary, E. villosa is tolerant to considerable amounts of environmental stressors, making suppression difficult, as it can germinate, sprouting seed-producing tillers throughout the growing season even when the main stem is dead or its roots are damaged, and, most worrisome of all, it presents a natural tendency towards herbicide resistance. Thorough and effective integral control programs based on new, accurate information are necessary to achieve these ideals.

Nevertheless, research should be conducted to study it better and determine whether the uncovered characteristics may be used to benefit humanity by producing medicine or for it to be safely used as fodder or forage without leading to further spread.